**4. Targeting long-lived plasma cells**

In SLE-prone mice, long-lived plasma cells (LLPCs) are present in the spleen and bone marrow, before week 4 [33] and contribute to the production of autoantibodies before the onset of symptoms. In SLE patients, long-lived plasma cells play a crucial role not only in the pathogenesis but also in the sustainment of autoimmunity and are unresponsive to standard B-cell depletion treatment by rituximab [34]. Treatment regimens, such as the combination of rituximab and belimumab [35], work toward this direction.

#### **4.1 Daratumumab**

Daratumumab is an anti-CD38 monoclonal antibody used in the treatment of multiple myeloma as well as in the treatment of AL amyloidosis [36]. It has been successfully administrated in two patients with refractory SLE [37]; belimumab was used as maintenance therapy, and treatment response was sustained during the 12-month follow-up period. The success of daratumumab was due to its pleiotropic effect in SLE patients: it eliminates LLPCs while leading to a reduction to interferon type I activity and reduction of CD19n B-cells. This observation led to the DARALUP study, a monocenter, open-label Phase II trial for refractory SLE patients [38].

#### **5. IFN**

#### **5.1 Rationale for INF antagonists use in SLE**

Interferon is a key cytokine in the pathogenesis of SLE. Interferon (IFN) signature genes are highly expressed in the peripheral blood of SLE patients [39], and interferon-inducible gene expression is associated with disease activity and lupus nephritis [40, 41]; high levels of ultrasensible IFN-a equally seem to be related with a higher risk of relapse in patients with quiescent SLE [42]. There are multiple biological therapies targeting IFN under investigation.

#### **5.2 Anifrolumab**

Anifrolumab is a human monoclonal antibody binding the IFN-I receptor subunit 1, inhibiting IFN-I signaling. It is the second biological therapy to be approved by FDA in SLE patients following the TULIP-1 [43] and TULIP-2 trials [3]. TULIP-1 [3] was a phase 3, double-blind, RCT of adults with moderate to severe SLE despite standard-of-care treatment, where patients were randomized to receive anifrolumab in two treatment regimens or placebo; the primary endpoint of SRI-4 at week 52 was not met, but a clinical benefit was observed in the anifrolumab group in terms of steroid sparing effect, skin lesions (as assessed by Cutaneous Lupus Erythematosus Disease Area and Severity Index (CLASI)) and British Isles Lupus Assessment Group–based Composite Lupus Assessment (BICLA) response. In TULIP 2 [3], patients were assigned to receive anifrolumab at 300 mg every 4 weeks or placebo; the primary endpoint of BICLA response at week 52 was achieved (47.8% in the anifrolumab group and 31.5% in the placebo group, p = 0.001). In a phase II trial assessing anifrolumab in association with mycophenolate mofetil and steroids, in patients with active proliferative LN [44], the primary endpoint of change in baseline 24-hour urine protein-creatinine ratio (UPCR) at week (W) 52 was not met, but there were encouraging though nonstatistically significant results in the anifrolumab group in complete renal response and corticoid sparing effect. Patients with high interferon signature genes were more likely to reach BICLA response at week 52 according to a post-hoc analysis [45]. In terms of safety, there was an increased risk of herpes zoster in the anifrolumab group [3, 44].

#### **6. Other interferon targeting therapies**

Rontalizumab is a human anti-IFN-α monoclonal antibody neutralizing all 12 IFN-α subtypes; it was assessed in SLE patients with active SLE in the ROSE trial [46], failing to reach the BILAG and SRI-4 primary and secondary endpoints at week 24. Sifalimumab is a human, IgG1 κ monoclonal antibody that neutralizes the majority of IFN-α subtypes [47]; despite the encouraging results of a phase IIb RCT, meeting the primary endpoint of SRI-4 response at week 52, the clinical trials were halted.

IFN-a kinoid is an immunotherapeutic vaccine composed of inactivated recombinant human IFN-α2b coupled to a T-helper carrier protein (keyhole limpet hemocyanin). Its aim is to induce antibodies against IFN by active immunization, thus reducing the expression of IFN-induced genes [48]. This hypothesis was confirmed *Targeted Therapies for Systemic Lupus Erythematosus (SLE): A Critical Appraisal DOI: http://dx.doi.org/10.5772/intechopen.105811*

in transgenic mice expressing human IFNα2b [49]. The efficacy and safety of IFN-K were evaluated in a phase IIb, randomized, double-blind, placebo-controlled trial in adults with active systemic lupus erythematosus (SLE) and positive interferon gene signature [44]. The primary endpoints were neutralization of IFN gene signature and the BICLA at week 36 modified by mandatory corticosteroid (Cs) tapering. At week 36, 91% of the patients receiving IFN-K had neutralizing IFN antibodies and reduced IFN signature; on the contrary, the clinical primary endpoint of BICLA at week 36 was not met; of note 53% of the treated patients attained LLDAS at week 36 (vs 30% in the placebo group, p = 0.0022). IFN-K had also a significant corticoid sparing effect.

#### **6.1 JAK inhibitors**

Janus kinases (JAKs) and signal transducers and activators of transcription (STATs) are responsible for signal transduction of multiple cytokines and growth factors in different cell types [50]. The JAK/STAT pathway is involved in the maintenance of immune tolerance; thus, JAK/STAT dysregulation is implicated in many autoimmune diseases [51] and is an attractive treatment target. JAK inhibitors are already used in multiple rheumatic diseases such as rheumatoid arthritis (RA), ankylosing spondylitis (AS), and psoriatic arthritis (PsA). There are many in vitro and in vivo studies supporting the involvement of JAK/STAT pathway in SLE [52]. Of note, the STAT4 gene polymorphism has been associated with SLE susceptibility and renal disease [53].

Tofacitinib a JAK 1 and 3 inhibitor was evaluated in a phase I trial in SLE patients [54]. Tofacitinib was found not only to be safe but also improved cardiometabolic and immunologic parameters associated with the premature atherosclerosis and decreased IFN I gene signature.

Baricitinib is a selective JAK 1 and 2 inhibitor; in a phase II double-blind placebocontrolled RCT, it proved to be safe and effective at the dose of 4 mg in the resolution of arthritis or rash at week 24 [55]. In murine models, baricitinib ameliorated renal inflammation and led to the recovery of the expression of structural proteins in podocytes [56], indicating its potential role in the treatment of LN.

Solcitinib, a selective JAK 1 inhibitor, was evaluated in a phase II study in patients with active, extra renal SLE [57]. The study terminated due to absence of significant effect on mean IFN transcriptional biomarker expression (all panels, 50 patients). Safety data showed elevated liver enzymes in six patients (one confirmed and one suspected case of drug reaction with eosinophilia and systemic symptoms), leading to immediate dosing cessation.

Filgotinib, a Janus kinase 1 inhibitor, and lanraplenib, a spleen kinase inhibitor, have been assessed in patients with cutaneous lupus erythematosus (CLE) [58]. In a phase II trial, the primary endpoint of change from baseline in Cutaneous Lupus Erythematosus Disease Area and Severity Index Activity (CLASI-A) score at week 12 was not met; two serious adverse events (SAE) (one major cardiovascular event and hypersensitivity) were reported in the lanraplenib group and one SAE in the filgotinib group. Filgotinib and lanraplenib were also evaluated in patients with lupus membranous nephropathy [59]. The study included only nine patients, of whom only four in the filgotinib group and one in the lanraplenib group completed week 16; in the filgotinib group, all four patients had a median reduction of 50.7% in 24-hour urine protein. Further research is necessary before drawing any conclusions.

#### **7. Other cytokine-targeted therapies**

Cytokine production is distinct in patients with SLE compared with patients with other rheumatic diseases and may change during disease course and different SLE phenotypes [60]. There are multiple cytokines not only inflammatory (interferons type I and II, IL-6) but also immunomodulatory (such as IL-10 and TGF-β), implicated in the pathogenesis of the disease [61].

#### **7.1 Targeting Interleukine-6**

Interleukine 6 (IL-6) is a cytokine with pleiotropic effects in different target cells [61, 62]. In SLE patients there is an increased production and increased serum levels of IL-6 [63]. IL-6 seems to be implicated in lupus nephritis [64] and has an active role in mesangial proliferative glomerulonephritis [65]. Studies also suggest that IL-6 is implicated in an autocrine manner in maintaining B-cell hyperactivity [66].

Tocilizumab is a humanized mAb against the IL-6 receptor (IL-6R). In SLE patients, it was assessed in an open-label phase I dosage-escalation study [67] in 16 patients with mild-to-moderate disease activity in three treatment regimens: 2 mg/kg, 4 mg/kg and 8 mg/kg every 2 weeks, with a good clinical and serological response in approximately half of the patients; neutropenia occurred in all three groups with two grade III neutropenia in the 8 mg/kg group.

Sirukumab is a human, anti-IL-6 monoclonal antibody binding to IL-6 with high affinity and specificity. It has been evaluated in a phase I trial in 31 patients (23 treated with sirukumab) with cutaneous lupus erythematosus (CLE) and 15 patients with SLE (10 treated with sirukumab), with a good tolerance, but with some cases of neutro-, lympho-, or thrombocytopenia in the sirukumab group [68]. Its efficacy was also assessed in a phase II trial in patients with active proliferative lupus nephritis with persistent proteinuria despite standard of care [69], with disappointing results.

PF-04236921, a fully human immunoglobulin G2 monoclonal antibody, failed to prove its efficacy in lupus in phase II trials [70].

#### **7.2 Interleukin 17**

Interleukin 17 is a pro-inflammatory cytokine implicated in the pathogenesis of various RMDs. In SLE, the IL-17 axis seems to promote autoantibody production, immune complex deposition, and complement activation leading to tissue damage [71]. In patients with SLE, there is an increased number of Th17 cells as well as high serum levels of IL-17A, correlated with disease activity [72]. IL-17 seems to be implicated in lupus nephritis [73].

Secukinumab, a human IgG1κ monoclonal antibody, is actually assessed in a phase III trial in combination with standard of care in patients with proliferative LN [74].

#### **7.3 Interleukin 12/23 axis**

Τhe IL23/L17 axis plays a fundamental role in multiple autoimmune diseases. In patients with active SLE, there is an upregulation of serum IL-23 and IL-23 receptor compared with healthy controls, and IL-23 seems to limit in vitro IL-2 production, leading to the promotion of autoimmunity [75]. On the other hand, IL-12 through the ILL-12-STAT4 axis is also involved in lupus pathogenesis inducing both IFN-γ and IL-21 by human CD4 + T cells [76]; of note, STAT4 is one of the most dominant risk alleles in SLE [77].

#### *Targeted Therapies for Systemic Lupus Erythematosus (SLE): A Critical Appraisal DOI: http://dx.doi.org/10.5772/intechopen.105811*

Ustekinumab is a fully human monoclonal antibody directed at the p40 subunit shared by the cytokines IL12 and IL23; in a phase 2 RCT in patients with active SLE, it resulted in higher rates of SRI-4 response in addition to standard of care at week 24 compared with placebo (p = 0∙006) [78].

#### **7.4 Low-dose IL-2**

Regulatory T-cells (Tregs) under the influence of interleukin 2 (IL-2) play a crucial role in the maintenance of immune tolerance; in SLE patients there is an acquired deficiency in IL-2 leading to defects of Tregs [79]. Low-dose IL-2 corrects defects in Tregs in patients with SLE leading to restoration of immune tolerance [80]. Its potential role in clinical practice has been evaluated in two RCTs [81, 82] with a good safety profile and clinical response resulting to complete remission in seven patients with LN (53.85%, compared with 16.67% in the placebo group, p = 0.036).

#### **7.5 T-cell strategies**

In SLE, T cells are chronically active due to T-cell receptor rewiring, hypomethylation of genes related to cell activation, and mTORC1 activation [83] and are implicated in SLE pathogenesis through interaction with B-cells by enhancing the production of autoantibodies, promotion of B-cell differentiation, proliferation, and maturation [84]. Multiple T-cell strategies have already been evaluated in SLE patients.
